Sound-insulating polyurethane elements save weight

A purr rather than a rattle

The progress made by modern engineering in car design can also be recognized by the human ear.

Intelligent acoustic design has meant not only that car doors nowadays shut with a solid clunk rather than a slamming noise, but also that drivers are hardly bothered at all by the noise of the engine. For this development we can thank above all the sound-absorbing material composites made of polymeric materials that are used, for example, in bulkhead linings for diesel vehicles. These linings were developed by Bayer MaterialScience, a subgroup of Bayer AG, in cooperation with acoustics specialist, Carcoustics International GmbH, both based in Leverkusen, Germany. The parts are made of highly filled Bayflex® SA (sound-absorbing) RIM material, back-foamed with Bayfit® SA, Bayer's sound-insulating flexible polyurethane foam. Using the RIM process, this design-friendly, noise-insulating material combination can be easily adapted to the specific conditions inside the car.
"Using a flexible foam on its own as an insulating material will not get you very far when it comes to absorbing engine noise," explains Andreas Stumpf from Bayer MaterialScience. "To effectively suppress all noise frequencies, you also need a highly filled bulk system of comparatively heavy material in addition to the flexible foam system. This requirement naturally contradicts the efforts being made to reduce overall vehicle weight, but we believe that, with our Bayflex® SA system, we have now developed a more intelligent solution that does not buck the trend towards fuel-saving cars with an optimized center of gravity." On the subject of noise reduction, he continues: "Tests under simulated service conditions, in which the Bayflex®/Bayfit® combination was compared with other materials currently being used as standard on car production lines, showed a significant reduction in noise levels of 3 dB in the car interior."